The invention relates to a method for operating a spark ignition internal-combustion engine with an exhaust gas turbocharger.
With respect to the technical environment, reference is made, for example, to WO 2009/036992 A1 and WO 2011/015336 A1. In particular, from WO 2011/015336 A1, a spark ignition piston internal-combustion engine with a combustion chamber is known, which has a piston that is movably arranged therein and which is mechanically operatively connected with a crankshaft. The combustion chamber has an inlet valve and an outlet valve. The valves are mechanically operatively connected by way of a camshaft with the crankshaft such that they are opened and closed once respectively per two stroke cycles of the piston; i.e. it is a 4-stroke internal-combustion engine. Furthermore, a fluid-dynamic device is provided which is used for increasing a pressure in an inlet volume in front of the combustion chamber. The fluid-dynamic device is operatively connected with the combustion chamber by way of the inlet valve. Furthermore, the piston internal-combustion engine has a device for the fuel injection as well as a throttle valve which is used for influencing the pressure in the inlet volume. The combustion chamber further has an additional charge valve, which connects the combustion chamber with a compressed-air tank, the charge valve being operatively connected by way of the camshaft with the crankshaft. In addition, there is a mechanism, which is used for interrupting the mechanical operative connection between the charge valve and the crankshaft, so that the charge valve can be closed during several stroke cycles of the piston.
This known piston internal-combustion engine has the disadvantage of being a highly complex overall system with high resulting costs.
A similar device for bridging the turbo lag of a diesel internal-combustion engine is known, for example, from European Patent document EP 1 856 388 B1. In contrast to WO 2011/015336 A1, in this published patent application, the compressed-air tank is, however, filled with compressed air not by way of the combustion chamber inside the internal-combustion engine but by way of an external compressor driven by the crankshaft. Furthermore, the injection of compressed air does not take place directly into the combustion chamber of the piston internal-combustion engine but rather into an injection point in the suction pipe between the exhaust gas turbocharger and the combustion chamber. In the embodiment of European Patent document EP 1 856 388 B1, a turbocharged diesel combustion engine with six cylinders in series is therefore disclosed, whose suction pipes are connected to a manifold, and have a connection flange to which an inlet gas pipe section is connected with its second end connection for the discharge. The first end connection for the admission is coupled by a pipe with the discharge opening of the charge air cooler, whose admission opening is coupled by a pipe with the discharge opening of the turbo compressor. An air filter with a pipe is connected to the admission opening of the turbo compressor. The turbo compressor is part of the exhaust gas turbocharger, whose exhaust gas turbine is connected with its admission opening to the discharge opening of the exhaust manifold. The turbo compressor and the exhaust gas turbine are fastened to a common shaft. The combustion chambers are connected to the exhaust manifold by exhaust pipes. The discharge opening of the exhaust gas turbine is coupled to the exhaust pipe. The fuel supply to the cylinders takes place by injection nozzles whose automatic control is carried out by an electronic control unit. The connection of an accelerator pedal is connected to the connection of the electronic control unit. A further electric connection of the control unit is coupled to the electric connection of the inlet gas pipe section. The inlet gas pipe section has a compressed-air connection which is connected to the outlet connection of the compressed-air reservoir. The feeding connection of the compressed-air reservoir is connected by the pipe to the compressed-air connection of the air compressor. A pressure regulator and dehumidifier are built into the pipe. The air compressor has a suction piece which is equipped with an air filter. The shaft of the air compressor is connected by a belt drive with the crankshaft of the turbo-charged diesel internal-combustion engine
In order to improve the acceleration emission behavior, the following method is suggested in European Patent Document EP 1 856 388 B1:                a) Determining the torque demand signal and feeding the data to the electronic control unit;        b) determining the engine parameters and feeding the parameters to the electronic control unit;        c) determining the position of the throttle valve and feeding the parameters to the electronic control unit;        d) determining the air pressure in the interior of the intake gas pipe section between the first end connection and the throttle valve or the second end connection and the throttle valve and feeding the pressure values to the electronic control unit;        e) determining the air pressure in the interior of the suction pipe between the cylinder intake valve and the throttle valve and feeding the pressure value to the electronic control unit as well as determining the air pressure in the interior of the suction pipe between the throttle valve and the turbo compressor and feeding the pressure value to the electronic control unit,        f) processing the above data and measured values in the electronic control unit for generating actuation output signals for opening/closing the compressed-air valve of the temporary injection into the suction pipe, and        g) simultaneous actuating of the throttle valve at the start of the injection in the “close” direction and at the end of the injection in the “open” direction.        
This prior art has the disadvantage that the operating method is optimized for a self-ignition internal-combustion engine.
It is an object of the present invention to provide a method for operating a spark ignition internal-combustion engine with an exhaust gas turbocharger, while simultaneously minimizing the reaction time to a desired torque value jump of the internal-combustion engine with a minimal consumption of compressed air.
This and other objects are achieved by way of the method steps according to the invention.
As a result of the method according to the invention, the reaction time is clearly minimized to a desired torque value jump of the internal-combustion engine, while the compressed-air consumption is minimal.
In order to achieve this object, the following method is provided for operating a spark ignition internal-combustion engine with an exhaust gas turbocharger, the method including the acts of:                a) Increasing the torque demand on the internal-combustion engine,        b) opening of the air injection valve and constant measuring of the first and the second gas pressure p1, p2 by the control unit,        c) closing of the throttle valve by the control unit at the earliest with the opening of the air injection valve or as soon as the second pressure p2 exceeds the first pressure p1,        d) calculating of a first gas mass flow, which is delivered into the internal-combustion engine, and calculating of a second gas mass flow, which corresponds to the desired torque, by the control unit,        e) as soon as the first gas mass flow is greater than the second gas mass flow, displacing an ignition angle to late,        f) as soon as the first gas mass flow multiplied by a factor θzw,min is equal to the second gas mass flow, slow closing of the air injection valve,        g) as soon as the exhaust gas turbocharger has reached a defined rotational speed, complete closing of the air injection valve,        h) as soon as the first gas pressure p1 is equal to the second gas pressure p2, opening of the throttle valve by the control unit, and        i) conventional operating of the internal-combustion engine.        
If a compressor bypass, which can be closed by way of an overflow valve, for bypassing the compressor is provided in the intake air section for the compressor, the following additional method act is provided:                j) As soon as the compressor reaches a surge line, opening of the overflow valve by the control unit.        
Another further development of the method includes the act of:                k) Automatic controlling or a controlling of the overflow valve by the control unit such that the compressor will not exceed the surge line.        
By means of the two last-mentioned method acts (j) and (k), it is prevented that the compressor exceeds its surge line and, as a result of the pressure conditions, enters the surge range.
Another further development of the method according to the invention includes the following method act:                l) Constant controlling or automatic controlling of the fuel system by the control unit such that a near-stoichiometric fuel/air ratio of the internal-combustion engine will constantly be available for a combustion.        
By means of this process step according to the invention, it is prevented that, for example, unburnt hydrocarbons are emitted. The emissions of the internal-combustion engine can be minimized by the use of a 3-way catalytic converter. A near-stoichiometric fuel/air ratio is a fuel/air ratio in the range of approximately 0.97 to 1.03, which is considered to be stoichiometric in practical operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.